1. Technical Field
The present invention relates to a semiconductor integrated circuit, and in particular, to a data amplifying circuit.
2. Related Art
A semiconductor integrated circuit amplifies bitline signals using a bitline sense amplifier (hereinafter, referred to as “BLSA”) and transmits the amplified bitline signals through a local input/output line (LIO). The signals LIO/LIOb to be transmitted through the local input/output line usually have levels inverted with respect to each other.
An input/output sense amplifier (hereinafter, referred to as “IOSA”) amplifies the signals LIO/LIOb of the local input/output line and transmits the amplified signals through the global input/output line. The IOSA uses a two-stage amplification configuration that amplifies the signals LIO/LIOb of the local input/output line using a current mirror type amplifier, and then amplifies the signals to high and low levels using a cross coupled type amplifier. Alternatively, the IOSA may also use a one-stage amplification configuration that amplifies the signals of the local input/output line using only the cross coupled type amplifier and transmits the amplified signals through the global input/output line.
Generally, the load of the local input/output line is larger than the driving ability of the BLSA. Accordingly, the signals LIO/LIOb of the local input/output line that are input to the IOSA have low voltage levels.
A current mirror type amplifier amplifies a difference between two input signals by an amount corresponding to a gain characteristic to the amplifier. Accordingly, even though the difference between the two signals is small and the values of the two signals are instantaneously changed due to offset or noise, if the input signals return to a normal condition, the output of the amplifier also returns to a normal condition. Therefore, while the signals of the local input/output line can be amplified starting from when the difference between the two signals is small, an amplification level is small at that time. As a result, the high and low levels cannot be output.
In a cross coupled type amplifier, if the values of the two input signals are instantaneously changed, even if the two input signals return to the normal condition, the output may be erroneously amplified due to an amplification operation caused by internal feedback. Therefore, for normal operation, the amplifier needs to start to operate after the difference between the two input signals is sufficiently large.
When two-stage amplification configuration is used, the IOSA can use the advantages of the current mirror type amplifier and the cross coupled type amplifier together. For example, when the difference in the potential between the input signals transmitted through the local input/output line is small, the current mirror type amplifier first amplifies the difference between the input signals, and subsequently the cross coupled type amplifier additionally amplifies the amplified signal output from the current mirror type amplifier. Therefore, the output signal at the high and low levels is output.
When the two-stage amplification configuration is used, an operation speed is faster in a case where the current mirror type amplifier amplifies the difference in advance than in a case where the BLSA waits until the difference in the potential between the local input/output line becomes sufficiently large. Therefore, since the signals of the local input/output line are transmitted to the global input/output line, the total amplification speed is fast. In this case, however, a circuit area is large and power consumption increases.
When the IOSA uses the one-stage amplification configuration, the BLSA waits until a difference in potential between the signals of the local input/output line becomes sufficiently large. Therefore, a speed that the signals of the local input/output line are transmitted is slow through the global input/output line, while the circuit area is small and current consumption is low.
However, in a general semiconductor integrated circuit, upon design, one of an IOSA using the two-stage amplification configuration and an IOSA using the one-stage amplification configuration is selectively used according to the requirements, such as the operation speed, the area, and current consumption of the circuit. Meanwhile, a change in requirements may be needed after design is completed (for example, current consumption needs to be reduced even if the operation speed becomes slow). Thus, when the IOSA using the two-stage amplification configuration is substituted with the IOSA using the one-stage amplification configuration, there is no method of pre-testing trouble during the operation. Further, a change in the amplification configuration is accompanied by a new circuit arrangement.